1. Field of the Invention
The invention relates to a thread braking device for stopping a running thread, especially as it is used in a textile machine, such as a loom.
2. Description of the Prior Art
Several embodiments of thread braking devices are known. According to one of these embodiments as described in DE-A 31 48 151, the running thread is braked by clamping. For this purpose it is guided between a fixed and a movable braking jaw. The movable braking jaw is actuated by an electromagnet, which magnet is controlled by a thread braking control unit. It has also been proposed to replace the fixed jaw by a somewhat flexible steel ribbon. To open this thread braking device, a spring is used, which disengages the jaws when the electromagnet is not powered. A disadvantage of this embodiment lies in the fact that after a comparatively short period of operation of a few hours ridges are forming along the path of the thread, which are formed of depositions of fibrous material from the thread and of material used in the treatment of the thread. When the jaws are clamped together, they now rest on these ridges and fail to brake the thread efficiently. This leads to loose wefts and therefore to faults in the textile fabric.
In another embodiment according to CH 676 234 braking elements were therefore proposed that were mutually displaceable. In these braking elements the thread is not clamped but deviated and partially wound up for braking. For perfect braking, the thread has to be kept under a minimum tension. This can lead to an increased danger of damaging or breaking very fine, sensitive threads of wool or cotton.